The central objective of our present work is to contribute to the complete understanding of the mechanism by which the corneal endothelium pumps fluid across it. A model for some aspects of this mechanism has been proposed by us recently and will be tested with the information to be gathered. An extremely sensitive, automatic microinjection apparatus which allows accurate measurements of the rate of transendothelial fluid transport has been developed and will be used for that purpose. The rate of fluid movement generated by either the fluid pump itself or by an osmotic gradient across the endothelium, and the hydraulic conductivity, will both be determined and correlated by means of numerical methods with the transendothelial potential difference, resistance and impedance, and also with the intracellular potentials and the cellular electrical characteristics determined with intracellular microelectrodes. Surgical dissection of the entire stroma will be attempted by using an oscillating knife; such method might allow the determination of which ions are being transported by direct chemical measurements of ionic concentrations.